FIG. 1 illustrates an example of a rotor assembly 1 in which an impeller 2 has been press fit onto a shaft 3. Owing to tolerances associated with the manufacture of the impeller 2, the bore 4 into which the shaft 3 has been press fit is misaligned. The misalignment of the bore 4, which has been exaggerated for the purposes of illustration, adversely affects the performance of the compressor. In order to minimize possible misalignment, the impeller 2 and shaft 3 are typically manufactured using high-precision processes that achieve tight tolerances. However, high-precision manufacturing is expensive and precludes the use of certain materials and processes that are otherwise not capable of achieving the necessary tolerances.